Sudoku

How to play Sudoku online

1. Choose Easy, Medium or Hard. A fresh unique-solution puzzle loads in this tab. No account, and nothing is uploaded.
2. Tap or click a cell to select it. Fill it with 1–9 from the on-screen pad or your keyboard. Backspace, Delete or 0 clears a cell you filled (clue cells stay locked).
3. Use the arrow keys to move around the grid. Press N (or the Notes button) to toggle pencil marks: small candidate digits inside an empty cell.
4. When you want a reality check, press Check. It highlights conflicts in a row, column or 3×3 box, and marks entries that do not match the solution. Hint fills one empty cell correctly; Reset clears your entries but keeps the clues; New puzzle deals another board at the current difficulty.
5. Fill every cell correctly and a win message appears with your elapsed time. Start another whenever you like.

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Rules in one minute

Each row, each column and each of the nine 3×3 boxes must contain the digits 1-9 once. The grey locked cells are given clues; everything else is yours to deduce. There is always exactly one solution for the puzzles this page generates.

Tips that actually help

Scan for singles first: a cell with only one possible digit, or a digit that can sit in only one place in a row, column or box. Work from crowded areas: a box with six clues is easier than a sparse one. When you place a firm number, clear matching notes from its row, column and box (this tool does that automatically in normal mode).

If you stall, toggle Notes and mark candidates rather than guessing. Guessing early on Hard boards usually creates conflicts that are painful to unwind. Use Check sparingly as a coach, not a crutch: it is there to catch slips, not to play for you.

When notes help (and when they do not)

Notes shine on Medium and Hard, once you have placed the obvious singles and need to track pairs or triples. Mark candidates in a quiet stretch of the board, then look for a digit that appears only once among the notes in a unit: that is a hidden single.

On Easy boards, notes can slow you down. If a cell is almost certain, commit the number. If you have filled a cell and later want candidates instead, erase it first, turn Notes on, then tap the digits you still consider possible.

Difficulty, timer and privacy

Easy leaves more clues; Hard removes more while still guaranteeing a unique solution. Generation runs locally with backtracking: fill a complete grid, then dig out cells and keep only removals that leave one solution. The timer is a simple elapsed clock for your own interest; scores are not saved and there is no leaderboard.

FAQ

Is every puzzle solvable with logic only?

Yes. Each board has exactly one solution. Hard puzzles may need more careful candidate work, but you should not need to branch and pray.

What does Check show?

Conflicts (the same digit twice in a row, column or box) and entries that disagree with the hidden solution. Empty cells are counted in the status line but not painted.

Does Hint spoil the whole puzzle?

No. Hint fills a single empty cell, preferably the one you have selected, then you carry on. Use it when you are stuck on one square, not as an auto-solve.

Will this work on my phone?

Yes. The grid scales to the screen width and the number pad is built for taps. Rotate to landscape if you prefer a larger board.

Is my progress saved?

No. Refresh or close the tab and the board is gone. That keeps the game private and simple, ideal for a quick break.

Related: Games, Neon Pong, Bubble Pop, Fidget Spinner.